Hard vacuum rotary pumps which operate on the molecular principle include a rotor which rotates at high speed in a stationary stator. The molecule transport effect is generated at the periphery of the rotor which rotates at high speed by reflection of a large proportion of these molecules from the facing zone of the stator; the stator then returns a large proportion of the molecules received to the part of the rotor which is situated below and so on, so that the rotor and stator assembly generates a pressure ratio between the partial pressure of the gas on the discharge side and the pressure of the same gas on the suction side.
The need for a high rotation speed of the rotor sets a serious problem for its bearings which must be installed in the vacuum. It is known to use ball bearings which operate in a primary vacuum and a drive motor also installed in a vacuum. But with such a type of pump, the difficulty lies in properly lubricating, especially cooling the balls, the cage and the races of the bearing, while cooling is impaired by heating which is inherent to the electric motor used.
The present invention aims to remedy these drawbacks.